1. Technical Field
The present invention relates to an inerting method for preventing and/or extinguishing fire in which in a predefinable oxygen content which is lower than normal ambient air is set and maintained in the spatial atmosphere of an enclosed room.
2. Description of Related Art
The invention further relates to an inerting system to set and/or maintain a predefinable oxygen content in the spatial atmosphere of an enclosed room which is reduced compared to the normal ambient air, wherein the inerting system comprises a gas separation system which separates off at least a portion of the oxygen from an initial gas mixture containing nitrogen and oxygen and by so doing, provides a nitrogen-enriched gas mixture at the outlet of the gas separation system, and wherein the inerting system comprises a supply line system for supplying the nitrogen-enriched gas mixture to the enclosed room.
An inerting system of the above type particularly relates to a system to reduce the risk of and extinguish fires in a protected room subject to monitoring, wherein the protected room is continuously rendered inert for the purpose of preventing or controlling fire. The mode of action of such an inerting system is based on the recognition that the risk of fire in enclosed rooms can be countered by continuously lowering the concentration of oxygen in the respective area to a value of e.g. approximately 12-15% by volume in normal cases. At such an oxygen concentration, most combustible materials can no longer ignite. The main areas of application are in particular IT areas, electrical switchgear and distributor compartments, enclosed facilities as well as storage areas for high-value commodities.
A method as well as a device of the type cited at the outset is known from the EP 2 204 219 A1 printed publication. A return system is employed here to withdraw a portion of the ambient air from within the enclosed room and feed it to a mixing chamber. Fresh air is added to the portion of air withdrawn from the room in the mixing chamber. The gas mixture thus produced (initial gas mixture) is fed to a compressor to be compressed there and then channeled to a nitrogen generator. The nitrogen generator separates off at least a portion of the oxygen from the initial gas mixture provided, thus producing a nitrogen-enriched gas mixture at the outlet of the nitrogen generator. This nitrogenated gas mixture is thereafter piped into the enclosed room in order to lower the oxygen content of the room's spatial atmosphere to a predetermined inerting level or to maintain it at a preset inerting level.
In practice, the method of returning oxygen-reduced air employed in printed publication EP 2 204 219 A1 to enable a more effective nitrogen generation for fire protection purposes calls for a return method which is adapted as optimally as possible to the gas separation system employed. Care must in particular be taken that the initial gas mixture provided in the mixing chamber is always in an optimized state for the gas separation system to be employed. This requirement is especially applicable when a plurality of nitrogen generators with respectively associated compressors are employed as the gas separation system. Care must then in particular be taken that the respective suction action of each individual nitrogen generator has no impact on any of the other nitrogen generators. This method has to factor in that a nitrogen generator which uses membrane technology to separate gases needs to exhibit a constant suction action. On the other hand, when a nitrogen generator is employed which makes use of the above-described PSA technology or the above-described VPSA technology to separate gases, the fact that such a nitrogen generator can operate with pulsed suction action needs to be considered.
Particularly in large-volume areas such as for instance warehouses, it is frequently desired to use a plurality of nitrogen generators in parallel for setting and maintaining a predefined or predefinable inerting level, whereby it can occur that the nitrogen generators are based on different gas separation technologies. Such a case requires a costly and independent return line for each nitrogen generator from the enclosed room to the respective nitrogen generator in order to ensure the optimum operation of each nitrogen generator. This requirement leads to a relatively complex structure to the inerting system.
Starting from this problem as posed, the present invention is based on the task of further developing the inerting system known from the EP 2 204 219 A1 printed publication, respectively the inerting method known from the EP 2 204 219 A1 printed publication, such that a predefined inerting level can be set and maintained in the enclosed room in the simplest yet most efficient manner possible.
According to a first aspect of the invention related to the inerting method, an initial gas mixture containing oxygen, nitrogen and other components as applicable is provided in a mixing chamber, wherein a gas separation system separates off at least a portion of the oxygen from this initial gas mixture provided and by so doing, a nitrogen-enriched gas mixture is provided at the outlet of the gas separation system, and wherein this nitrogen-enriched gas mixture is piped into the spatial atmosphere of the enclosed room. A return line system connecting the enclosed room to the mixing chamber is provided to supply the initial gas mixture, wherein a fan mechanism is further provided to withdraw a portion of the ambient air from within the enclosed room, preferably in regulated manner, and feed it to the mixing chamber, wherein the withdrawn portion of the room's air is admixed with fresh air, preferably in regulated manner, by means of a fan mechanism provided in the fresh air-supply line system connected to the mixing chamber.
A further aspect of the invention with respect to the method provides for the fan mechanism provided in the return supply line system to be controlled such that the volume of air withdrawn from the room per unit of time and fed to the mixing chamber be set such that the difference between the pressure prevailing in the mixing chamber and the pressure of the external ambient atmosphere does not exceed a predefined or predefinable upper threshold nor fall short of a predefined or predefinable lower threshold.
A further aspect of the invention with respect to the method provides for the fan mechanism provided in the fresh air supply line system to be controlled such that the volume of fresh air mixed with the withdrawn volume of room air per unit of time is set such that the difference between the pressure prevailing in the mixing chamber and the pressure of the external ambient atmosphere does not exceed a predefined or predefinable upper threshold nor fall short of a predefined or predefinable lower threshold.
A further aspect of the invention relating to the inerting system provides for the inerting system to further comprise a mixing chamber, preferably a mixing chamber configured as a mixing tube, which serves to provide the initial gas mixture, wherein a first line system opens into the mixing chamber, with a portion of the spatial air from inside the enclosed room being withdrawn and fed to the mixing chamber through said first line system, and wherein a second line system opens into the mixing chamber, with fresh air being supplied to the mixing chamber through said second line system.
A further aspect of the invention with respect to the inerting system provides for the inerting system to further comprise a first fan mechanism controllable by a control unit in the first line system and a second fan mechanism system controllable by the control unit in the second line.
A further aspect of the invention with respect to the inerting system provides for the control unit of an inerting system provided with such a control unit to be designed so as to control the first fan mechanism such that the amount of air withdrawn from the room per unit of time and fed to the mixing chamber by means of said first fan mechanism can be set such that the difference between the pressure prevailing in the mixing chamber and the pressure of the external ambient atmosphere does not exceed a predefined or predefinable upper threshold nor fall short of a predefined or predefinable lower threshold.
A further aspect of the invention with respect to the inerting system provides for the control unit of an inerting system provided with such a control unit to be designed so as to control the second fan mechanism such that the volume of fresh air admixed to the spatial air withdrawn from the room per unit of time by means of said second fan mechanism can be set such that the difference between the pressure prevailing in the mixing chamber and the pressure of the external ambient atmosphere does not exceed a predefined or predefinable upper threshold nor fall short of a predefined or predefinable lower threshold.
A further aspect of the invention with respect to the inerting system provides for the inerting system to comprise a control unit which is designed to control the gas separation system such that the residual oxygen content of the nitrogen-enriched gas mixture is changed as a function of the oxygen content prevailing in the spatial atmosphere of the enclosed room at that respective moment.
The resulting preventative or extinguishing effect of this inerting method is based on the principle of oxygen displacement. As is generally known, normal ambient air consists of about 21% oxygen by volume, about 78% nitrogen by volume and about 1% by volume of other gases. In order to be able to effectively reduce the risk of a fire breaking out in a protected room, the concentration of oxygen in the respective room is lowered by introducing inert gas such as e.g. nitrogen. For most solids, a fire-extinguishing effect is known to occur when the percentage of oxygen falls below 15% by volume. Depending on the flammable materials contained within a protected room, a further lowering of the oxygen percentage to e.g. 12% by volume may be necessary. Thus, continuously rendering a protected room inert will also effectively minimize the risk of a fire breaking out in said protected room.
The inventive method, inerting system respectively, capitalizes on the knowledge that the nitrogen purity of the nitrogenated gas mixture provided at the outlet of the gas separation system, respectively the residual oxygen content of the nitrogenated gas mixture provided at the outlet of the gas separation system, has an effect on the so-called “drawdown time.” The term “drawdown time” refers to the length of time required to set a predefined inerting level in the spatial atmosphere of the enclosed room.
The specific knowledge capitalized on herein is that as nitrogen purity increases, the air factor of the gas separation system rises exponentially.
The term “air factor” refers to the ratio of the volume of initial gas mixture pro-vided the gas separation system per unit of time to the volume of nitrogenated gas provided at the outlet of the gas separation system per unit of time. A nitrogen generator will usually allow the arbitrary selection of any nitrogen purity desired at the outlet of the gas separation system, with this value able to be set on the nitrogen generator itself. Generally speaking, the lower the nitrogen purity is set, the lower the operating costs for the nitrogen generator will be. In particular, the compressor then only needs to run for a comparatively shorter period of time when providing a nitrogenated gas mixture at the set nitrogen purity at the outlet of the gas separation system.
With respect to the costs incurred to operate the inerting system to inert the room, however, other additional factors need to be taken into account. These particularly include the purge factors involved in displacing the oxygen in the spatial atmosphere of the enclosed room by means of the nitrogen-enriched gas mixture provided at the outlet of the gas separation system until the predefined inerting level is reached, respectively maintained. These purge factors particularly include the amount of nitrogenated gas provided by the gas separation system per unit of time, the spatial volume of the enclosed room, and the difference between the oxygen content prevailing in the spatial atmosphere of the enclosed room at that respective moment versus the oxygen content corresponding to the predefined inerting level. To be hereby considered is that in terms of the drawdown time, the nitrogen purity of the gas mixture provided at the outlet of the gas separation system, respectively the residual oxygen content of the nitrogenated gas mixture, likewise plays a crucial role, since the purging operation goes faster the lower the residual oxygen content in the nitrogenated gas mixture.
The term “gas separation system” as used herein is to be understood as a system which can effect the separation of an initial gas mixture comprising at least the components of “oxygen” and “nitrogen” into an oxygen-enriched gas as well as a nitrogen-enriched gas. The functioning of such a gas separation system is usually based on the effect of gas separation membranes. The gas separation system used in the present invention is primarily designed to separate oxygen from the initial gas mixture. This type of gas separation system is frequently also referred to as a “nitrogen generator.”
This type of gas separation system makes use of a membrane module or the like, for example, whereby the different components contained in the initial gas mixture (e.g. oxygen, nitrogen, noble gases, etc.) diffuse through the membrane at different speeds based on their molecular structure. A hollow fiber membrane can be used as the membrane. Oxygen, carbon dioxide and hydrogen have a high diffusion rate and because of that, escape from the initial gas mixture relatively quickly when passing through the membrane module. Nitrogen having a low diffusion rate percolates through the hollow fiber membrane of the membrane module very slowly and thereby concentrates when passing through said hollow fiber/membrane module. The nitrogen purity, the residual oxygen content respectively, of the gas mixture exiting the gas separation system is determined by the flow velocity. Varying the pressure and the volumetric flow rate allows the gas separation system to be adjusted to the required nitrogen purity and necessary volume of nitrogen. Specifically, the purity of the nitrogen is regulated by the speed at which the gas passes through the membrane (dwell time).
The separated oxygen-enriched gas mixture is usually concentrated and discharged into the environment at atmospheric pressure. The compressed, nitrogen-enriched gas mixture is provided at the outlet of the gas separation system. An analysis of the product gas composition ensues by measuring the residual oxygen content in volume percent. The nitrogen content is calculated by subtracting the measured residual oxygen content from 100%. In so doing, it needs to be considered that although this value is designated as the nitrogen content or the nitrogen purity, it is in fact the inert content as this component is not only comprised of just nitrogen but also other gas components such as for example noble gases.
The gas separation system, nitrogen generator respectively, is usually fed compressed air which has been purified by upstream filter units. It is in principle conceivable to use a pressure swing process (PSA technology) utilizing two molecular sieve beds to provide the nitrogen-enriched gas, wherein the two sieves are alternatingly switched from a filter mode to a regeneration mode, thereby yielding the flow of nitrogen-enriched gas.
As long as it is not imperative to have a continuous flow of nitrogen-enriched gas at the outlet of a pressure swing-operating nitrogen generator, just one molecular sieve bed can also be used which is alternatingly switched into an adsorption mode upon the application of pressure, during which the nitrogen-enriched gas is provided at the outlet, and thereafter into a desorption mode at lower pressure during which the oxygen-enriched air within the proximity of the molecular sieve bed can be purged off.
When a nitrogen generator utilizes for example a membrane technology, the process capitalizes on the general knowledge that different gases diffuse through materials at different speeds. In the case of nitrogen generators, the different diffusion rates of the principal components of air; i.e. nitrogen, oxygen and water vapor, are used to generate a flow of nitrogen, respectively nitrogen-enriched air. In detail, to technically realize a membrane technology-based nitrogen generator, a separation material through which water vapor and oxygen can readily diffuse, but which only affords a low diffusion rate for nitrogen, is applied to the outer surfaces of the hollow fiber membranes. When air flows through the inside of such a treated hollow fiber, the water vapor and oxygen quickly diffuse outward through the hollow fiber wall while the nitrogen is largely retained within the fiber such that a strong concentration of nitrogen builds up during passage through the hollow fiber. The effectiveness of this separation process essentially depends on the flow rate in the fiber and the pressure differential over the hollow fiber wall. With a decreasing flow rate and/or a higher pressure differential between the interior and the exterior of the hollow fiber membrane, the purity of the resultant nitrogen flow increases. Generally speaking, a membrane technology-based nitrogen generator can thus regulate the degree of nitrogenization to the nitrogenated air provided by the nitrogen generator as a function of the dwell time of the compressed air provided by the compressed air source in the air separation system of the nitrogen generator.
If, on the other hand, the nitrogen generator is for example based on PSA technology, specially-treated activated charcoal makes use of the different binding rates of the atmospheric oxygen and atmospheric nitrogen. The structure of the activated charcoal employed is thereby changed such that a large number of micropores and submicropores (d<1 nm) develop over an extremely large surface area. At this pore size, the oxygen molecules of the air diffuse into the pores substantially faster than the nitrogen molecules such that the air in the proximity of the activated charcoal becomes enriched with nitrogen. A PSA technology-based nitrogen generator can thus—as is also the case with a membrane technology-based generator—regulate the degree of nitrogenization to the nitrogenated air provided by the nitrogen generator as a function of the dwell time of the compressed air provided by the compressed air source in the nitrogen generator.
As described above, these types of PSA technology-based nitrogen generators need to be alternately operated in an adsorption mode and a desorption mode, whereby pressure has to be applied to the molecular sieve bed during the adsorption mode (filter mode) in order to ensure sufficient diffusion of oxygen molecules in the pores of the activated charcoal (carbon granules, CMS) for the generating process. Compared to the higher sieve bed pressure versus the ambient pressure during the adsorption phase, the pressure is reduced during the subsequent desorption phase (purge or regeneration phase) in order to enable effective purging of the carbon granules.
Standard PSA nitrogen generators, which are also called pressure swing adsorption generators for this reason, use a pressure level substantially corresponding to the ambient pressure during the regeneration cycle (desorption phase). Compared to such standard pressure swing adsorption generators, so-called vacuum pressure swing adsorption generators (VPSA technology) are of more complex configuration, their desorption process is thereby intensified, respectively shortened, by the fact that not only is the pressure reduced to the level of the ambient pressure but also a pressure approaching a vacuum pressure level, which is lower than the ambient pressure, is actively established in the proximity of the molecular sieve bed to be regenerated. To do so, it is then necessary to provide, in addition to the increased pressure level provided by the compressor, also a corresponding reduced pressure approaching a vacuum pressure level, for which a vacuum source is usually needed. Such a vacuum source can be in the form of a vacuum pump, for example.
As indicated above, the inventive solution makes use of the knowledge that the air factor of the gas separation system increases exponentially with increasing nitrogen purity on the one hand and, on the other, that in order to set a predefined inerting level, the compressor used in the inerting system has to run for a longer period of time the lower the difference is between the oxygen content prevailing in the spatial atmosphere of the enclosed room at that respective moment and the residual oxygen content in the nitrogenated gas mixture. It is hereby to be taken into account that the power consumption of the inerting system is virtually directly proportional to the length of time the drawdown process takes to render a room inert, whether when setting the room at a fixed residual oxygen content or when lowering to a new reduced level, since the compressor upstream of the gas separation system is digitally driven to its operating point at optimum efficiency.
It thus remains to be noted that—when a lower value of e.g. only 90% by volume is selected for the nitrogen purity—the inert gas system has to run for a relatively long period of time in order to set an inerting level. Should the nitrogen purity value be raised for example to 95% by volume, the difference between the oxygen content of the inerting level to be set and the residual oxygen content of the gas mixture provided at the outlet of the gas separation system likewise increases, which thereby reduces the amount of runtime the compressor needs to set an inerting level, and thus lowers the power consumption of the inerting system. However the circumstance of increasing the nitrogen purity at the outlet of the gas separation system inevitably also increases the air factor. The circumstance has a negative effect on the runtime of the compressor necessary to set an inerting level, respectively the power consumption of the inerting system. This negative effect prevails if the increase in the air factor due to increasing the nitrogen purity becomes appreciable.
Unlike with the usual systems known from the prior art where a fixed value is selected for the nitrogen purity of the gas separation system, the present invention is based on an inerting system in which, when the enclosed room is being rendered inert, the residual oxygen content provided at the outlet of the gas separation system and the nitrogen-enriched gas mixture is preferably automatically or selectively adjusted to the oxygen content prevailing at that respective moment in the spatial atmosphere of the enclosed room in order to thus set the nitrogen purity of the gas separation system to a value which is optimized in terms of the time required.
The phrase “time-optimized nitrogen purity value” as used herein refers to the nitrogen purity of the gas separation system, the residual oxygen content respectively, provided at the outlet of the gas separation system and the nitrogen-enriched gas mixture with which a defined inerting system, in which the volume of nitrogenated gas mixture able to be provided per unit of time is constant, assumes a minimum time period for lowering from a current oxygen content to a predefined oxygen content corresponding to a given inerting level.
Being able to set the volume of room air withdrawn from the room per unit of time and fed to the mixing chamber and/or the volume of fresh air added to the withdrawn portion of the room air per unit of time such that the difference between the pressure prevailing in the mixing chamber and the ambient atmospheric pressure does not exceed a predefined or predefinable upper threshold nor fall short of a predefined or predefinable lower threshold ensures that the initial gas mixture provided at the outlet of the mixing chamber is always in a defined state and optimally adapted to the gas separation system. The inventive solution in particular allows gas separation systems utilizing a plurality of nitrogen generators, whereby said plurality of nitrogen generators can also be based on differing gas separation technologies. Particularly ensured with the inventive solution is that the respective suction action of the plurality of nitrogen generators applicably employed will not interact with the other nitrogen generators provided. It is therefore readily feasible for the inventive solution to also be employed as a fire extinguishing system or a fire prevention measure in large-volume rooms, for instance warehouses, by using multiple and potentially different nitrogen generators therein for the gas separation, without the need for a costly, independent and regulated return line for each nitrogen generator from the protected room to the respective nitrogen generator. Accordingly, the adapted return method proposed by the inventive solution avoids increased expenditure in realizing the inventive inerting system.
The solution according to the invention in particular also lowers the operational costs required to produce the inerting effect in a simple to realize yet effective manner, in particular also in the case of relatively large-volume rooms such as warehouses, for example.
A further aspect of the invention provides for the upper pressure differential threshold to be 1.0 mbar, preferably 0.5 mbar, whereby the lower pressure differential threshold is preferably 0.0 mbar. Having the difference between the pressure prevailing in the mixing chamber and the external atmospheric pressure being within this indicated range always ensures that the respective suction action of the nitrogen generators employed (a constant suction action for a nitrogen generator which uses membrane technology for the gas separation or a pulsed suction action for a nitrogen generator which uses PSA or VPSA technology for the gas separation) will be a non-interacting action. Of course other values are also conceivable for the upper and/or lower threshold.
A further aspect of the invention provides for a control unit-regulated first fan mechanism in a first line system via which a portion of the spatial air contained within the enclosed room is withdrawn from the room in a manner regulated by said control unit and fed to the mixing chamber. Of further advantage is the providing of a second control unit-regulated fan mechanism in a second line system, via which fresh air is supplied to the mixing chamber in regulated fashion. The control unit should thereby be designed to control the first and/or second fan mechanism such that the volume of spatial air withdrawn from the room per unit of time is identical to the volume of the nitrogen-enriched gas mixture which is supplied to the spatial atmosphere of the enclosed room per unit of time. Providing the correspondingly controllable fan mechanisms can further maintain the difference between the pressure prevailing in the mixing chamber and the external ambient atmospheric pressure (within a certain control range) at a predefined or predefinable value in a simple to realize yet effective manner. This thus ensures that the initial gas mixture is provided to the respectively utilized nitrogen generators of the gas separation system in an optimally adapted state.
According to a further aspect of the invention, the volume of fresh air which is admixed with the spatial air withdrawn from the room in the mixing chamber per unit of time is selected such that the volume of spatial air withdrawn from the room per unit of time is identical to the volume of the nitrogen-enriched gas mixture which is piped into the spatial atmosphere of the enclosed room per unit of time. This thereby ensures that no excess or negative pressure will develop by introducing the nitrogenated gas mixture into the spatial atmosphere of the enclosed room or by the discharging/return of the spatial air from the enclosed room respectively.
To provide the initial gas mixture, a further aspect of the invention provides for a mixing section into which open the first line system, through which a portion of the air contained in the enclosed room is withdrawn from the room in regulated manner, and the second line system, by way of which fresh air is supplied in regulated manner, preferably by means of a Y-connector. This mixing section is either integrated into the mixing chamber or upstream of the mixing chamber. The mixing section serves to mix the spatial air withdrawn from the enclosed room with the fresh air as supplied and is configured—in order to ensure optimum mixing—so that a turbulent flow will occur in the mixing section. To this end, it is conceivable to correspondingly reduce the mixing section's effective flow cross-section such that a flow rate is set for the fresh air introduced into the mixing section and the return room air likewise introduced into the mixing section which is greater than the characteristic Reynolds number-dependent limiting velocity. Alternatively or additionally hereto, it is conceivable to provide spoiler elements in the mixing section in order to induce a turbulent flow in said mixing section.
In the latter embodiment cited in which a mixing section is integrated into the mixing chamber or arranged upstream of the mixing chamber for the turbulent mixing of the return room air and the supplied fresh air, a further aspect of the invention provides for the mixing section to exhibit a length sufficiently long enough to effect the most complete and even mixing of the return room air and supplied fresh air as possible. It is particularly preferred here for the mixing section to be of a length which is at least five times that of the mixing section's hydraulic diameter. The hydraulic diameter is a theoretical dimension for calculations related to tubes or channels of non-circular cross sections. This term then allows making calculations as with a round tube. It is the quotient of four times the flow cross section and the wetted perimeter (inner and outer as applicable) of a measurement cross section.
A further aspect of the invention provides for the gas separation system to comprise at least one and preferably a plurality of nitrogen generators each associated with a respective compressor connected to the mixing chamber by means of a line system. The residual oxygen content provided at the outlet of the nitrogen generator and the nitrogen-enriched gas mixture is adjustable for each nitrogen generator by means of the control unit. This realization is in particular suitable for protecting large volume areas such as for instance a warehouse.
A further aspect of the invention provides for the gas separation system's at least one nitrogen generator, at least one of the plurality of nitrogen generators respectively, to be configured as a vacuum pressure swing adsorption generator; i.e. in other words, one which functions according to VPSA technology. In the case of such a vacuum pressure swing adsorption generator, a line system is additionally provided between the mixing chamber and at least one inlet of the vacuum pressure swing adsorption generator. A controllable intermediate valve having a control connection to the control unit is active in this line system. The control unit can thus effect a direct controllable connection between the mixing chamber and the at least one inlet of the vacuum pressure swing adsorption generator. In conjunction with the method according to the invention, it is then provided that during the desorption phase of the vacuum pressure swing adsorption generator and for example a few seconds before the desorption phase is scheduled to end, for example five seconds before the scheduled end of the desorption phase, the intermediate valve in the line system connecting the mixing chamber and the nitrogen generator is brought from a closed position into an open position allowing passage so that the mixing chamber is directly connected to at least one inlet of the vacuum pressure swing adsorption generator prior to the end of the vacuum pressure swing adsorption generator's desorption phase.
A further aspect of the invention provides for the nitrogen generator of the gas separation system configured as a vacuum pressure swing adsorption generator to comprise at least one inlet, wherein the at least one inlet is selectively connected to the pressure side of a compressor or to the suction side of a vacuum source by means of a line system.
According to a further aspect of the invention with a nitrogen generator of the gas separation system configured as a vacuum pressure swing adsorption generator having at least one inlet, the at least one inlet of the nitrogen generator is connected to the suction side of the vacuum source during a desorption phase.
According to a further aspect of the invention with a nitrogen generator of the gas separation system configured as a vacuum pressure swing adsorption generator, at least one inlet of the nitrogen generator is selectively connected to the mixing chamber by means of a line system.
According to a further aspect of the invention with a nitrogen generator of the gas separation system configured as a vacuum pressure swing adsorption generator having at least one inlet, the at least one inlet of the nitrogen generator is connected to the mixing chamber by means of a line system to end a desorption phase of the nitrogen generator.
Since a negative pressure prevails at this inlet of the vacuum pressure swing adsorption generator during the desorption phase, nitrogen-enriched air from the mixing container is automatically provided into this inlet of the vacuum pressure swing adsorption generator prior to the end of the desorption phase, which leads for example to an adsorption bed containing carbon granules (CMS). A passive increase in pressure thus occurs in such an adsorption bed (CMS container) so that the desorption phase for this vacuum pressure swing adsorption generator can be passively ended without any additional expenditure of energy which saves time and energy compared to conventional solutions. Furthermore, when the pressure swing adsorption generator is then thereafter switched into a subsequent adsorption operation, such a passive increase in pressure in the adsorption bed (CMS container) enables the vacuum pressure swing adsorption generator to be switched into adsorption operation possible without the compressor load that would otherwise be necessary to regenerate a pressure in the area of the adsorption bed for the subsequent adsorption operation which is closer to the excess pressure subsequently created during the adsorption phase. What this realizes is that the compressor associated with the vacuum pressure swing adsorption generator can bring the molecular sieve bed back to the operating pressure in a shorter amount of time, whereby nitrogen is then in turn generated faster at the outlet of the vacuum pressure swing adsorption generator. Moreover, because air which is already nitrogenated flows from the mixing chamber toward the molecular sieve bed, the oxygen level during the subsequent adsorption phase already starts at a lower level. The appropriate design to the mixing chamber, for example preferably as a long mixing tube, in turn yields advantageous pressure fluctuation-compensating properties so that even the early end of a pressure equalization procedure in such a desorption phase of the vacuum pressure swing adsorption generator will not have any impact on for example any other of the plurality of nitrogen generators. In other words, ensuring the continued non-interacting operation of all the nitrogen generators employed.
With respect to the mixing chamber employed in the inventive solution, a further aspect of the invention provides for said mixing chamber to exhibit a volume which is dependent on the number of nitrogen generators used in the inerting system and/or on the principle on which the functioning of the least one nitrogen generator is based. The volume of the mixing chamber is to in particular be selected such that the respective suction action of the nitrogen generators employed will be a non-interacting action for all nitrogen generators.
In accordance with a further aspect of the invention, the mixing chamber is hereby further configured such that the maximum flow rate which can occur in the mixing chamber is less than 0.1 m/s on average. This is attained by suitably selecting the mixing chamber's hydraulic cross section.
A further aspect of the invention provides for the residual oxygen content of the nitrogen-enriched gas mixture, the nitrogen purity of the gas separation system respectively, to preferably be set automatically according to a predetermined characteristic curve.
A further aspect of the invention provides for such a characteristic curve to specify the time-optimized behavior of the residual oxygen content in the nitrogenated gas mixture in relation to the oxygen content in the spatial atmosphere of the enclosed room, according to which the inerting process can set a predefinable reduced oxygen content in the spatial atmosphere of the enclosed room compared to the normal ambient air in the shortest amount of time.
The phrase “time-optimized behavior of the residual oxygen content” refers to the time-optimized value of the residual oxygen content dependent on the oxygen content in the spatial atmosphere of the enclosed room. As indicated above, the time-optimized value of the residual oxygen content corresponds to the value of the residual oxygen content to be selected for the gas separation system such that the inerting method can set a predefinable oxygen content in the spatial atmosphere of the enclosed room which is reduced compared to the normal ambient air within the shortest amount of time.
The characteristic curve, according to which the residual oxygen content is set as a factor of the oxygen content prevailing at that respective moment in the spatial atmosphere of the enclosed room is predetermined (measured or calculated) for the gas separation system/inerting system.
Since one aspect of the inventive solution relates to the setting of the nitrogen purity of the gas separation system, or the residual oxygen content in the nitrogen-enriched gas mixture respectively, as a function of the oxygen content prevailing in the spatial atmosphere of the enclosed room at that respective moment and according to a further aspect of the inventive solution, the nitrogen purity of the gas separation system, the residual oxygen content in the nitrogen-enriched gas mixture respectively, is automatically set as a function of the oxygen content prevailing in the spatial atmosphere of the enclosed room at that respective moment so as to thereby be able to render the room inert at the lowest possible operating costs, a further aspect of the invention provides for either directly or indirectly measuring the current oxygen content in the spatial atmosphere of the enclosed room continuously or at predefined times and/or upon predefined events. A further aspect of the invention then further provides for setting the residual oxygen content in the nitrogen-enriched gas mixture to a predefined, time-optimized value continuously or at predefined times and/or upon predefined events. This predefined, time-optimized value is to correspond to a residual oxygen content at which the inerting method can lower the oxygen content in the spatial atmosphere of the enclosed room to a predefined drawdown value based on the respectively current oxygen content within the shortest amount of time possible.
A further aspect of the inventive solution provides not only for the nitrogen purity of the gas separation system to be changed as a function of the oxygen content prevailing at that respective moment in the spatial atmosphere of the enclosed room, but the oxygen content in the initial gas mixture is also changed as a function of the oxygen content prevailing in the enclosed room's spatial atmosphere at that respective moment. Doing so makes use of the knowledge that the air factor of the gas separation system can be lowered when the initial gas mixture supplied to the gas separation system exhibits a reduced oxygen content.
Thus, for the purpose of providing the initial gas mixture, one aspect of the invention provides for the regulated withdrawing of a portion of the ambient air from within the enclosed room and the regulated supplying of fresh air to the withdrawn portion of the room's air. So as to thereby prevent the pressure inside the enclosed room from changing by the supplying of nitrogen-enriched gas or by the drawing off a portion of its ambient air, the volume of fresh air admixed to the ambient air withdrawn from the room is selected such that the volume of ambient air withdrawn from the room per unit of time is identical to the volume of nitrogen-enriched gas mixture provided at the outlet of the gas separation system and piped into the spatial atmosphere of the enclosed room per unit of time.
The following will make reference to the accompanying drawings in describing exemplary embodiments of the inventive inerting system.